202 



HENRY LAURENS 



TABLE 3 

 Reactions of eyeless Amblystoma to local skin illumination 



REACTIONS 



REGIONS ILLUMINATED 



Head 



Mid-body 



Tail 



Directions of 



Number of responses. 

 Per cent of responses 



+ 



112 



56 



+ 



106 



53 



+ 



108 



54 







29 



15 



that a movement in its path toward or away from its source was 

 impossible. The percentages of indifferent reactions and of no 

 reactions within fifteen minutes were high as compared with the 

 results obtained when the entire eyeless animal was illuminated. 

 The head region in the normal larvae proved to be more sensitive 

 than the others, due to the fact that the retina was also illumi- 

 nated. In the blinded larvae there was no evidence that one re- 

 gion was more sensitive than the others, which is not in agreement 

 with the results of other investigators on other forms. Dubois 

 ('90) found the tail of Proteus to be the most sensitive region of 

 the skin, and both Reese ('03) and Pearse ('10) found the same for 

 Cryptobranchus. Reese also noted that the head of Necturus 

 was more sensitive than the tail, due probably to stimulation 

 received through the eyes, and Pearse showed that when the eyes 

 of Necturus were remo^'^ed the tail was the most sensitive region. 

 Eycleshymer ('08) also found that in both normal and decapi- 

 tated Necturus larvae the tail is the most sensitive region of the 

 skin. 



As has been seen the larvae of Amblystoma punctatum are 

 positively phototactic, both in the normal and eyeless condition. 

 The adults, on the other hand, are negative, both when normal 

 and when blinded (Pearse '10, p. 173). We have here then an 

 example of an animal changing the sense of its reaction to light 

 from positive to negative with its change from the larval stage 

 to the adult. 



The skin chromatophores of amphibian larvae have been shown 

 to present different conditions of expansion and contraction of 

 their pigment under different conditions of light and darkness. 



